Ultra-Dry Seed Storage Zeolite vs. Silica Gel Choosing the Right Desiccant for Seed Storage: Seed drying refers to reducing seed moisture to a safer level. It is basically done for the purpose of sustaining seed viability and longevity by minimizing attacks by storage pests and pathogens.

Ultra-dry seed storage

Ultra-dry storage, also known as low moisture content storage, is a technique for decreasing seed moisture content up to 5-6 per cartage. It is one of the best methods for storing seeds for a longer period by using desiccants in an air-tight container without affecting the seed quality.

Different Ultra drying methods are

1. Dry room or drying chamber
2. Desiccant – Silica gel/charcoal
3. Saturated salts / Lithium Chloride solutions
4. Air-conditioned room/vehicle
5. Incubator drier

Desiccants

• Desiccant is a hygroscopic substance that absorbs moisture from seeds by breaking the bond between seed and water molecules. Seed drying time and drying procedures depend on the initial seed moisture content, amount of seed, and dryness of the desiccant.
• Seeds of any species, at high moisture content, will dry in about 30 days in a typical dry room set at 10-15% RH and 10-25°C.

Types of desiccant

• Silica gel (Sodium silicate)
• Zeolite beads (Molecular sieves)
• Lithium chloride
• Calcium chloride
• Activated charcoal

Properties of the Desiccants

• Should be Reusable or Regenerative
• Should be Hygroscopic and water-insoluble
• Desiccants a Less cost-effective
• Should have long Durability
• Should be non-toxic to seeds
• Should be Eco-friendly  and non-toxic to human beings

Ultra-Dry Seed Storage Zeolite vs. Silica Gel: Difference between zeolite beads and silica gel

Zeolite beads	Silica gel
The drying process is slow and has no effect on seed quality.	The drying process is faster compared to beads, with a chance of damage to seed quality.
It takes a long time for the equilibrium of RH and temperature.	Less time is needed for the equilibrium of RH and temperature.
There is no loss of water-holding capacity after repeated heating for regeneration.	There is a loss of water-holding capacity after repeated regeneration.

PRINCIPLES OF DRYING BEADS:

• Drying beads absorb and hold the water molecules in their microscopic pores. Beads absorb water until their pores are filled, up to 20 to 25% of their initial weight (The initial weight of beads is 100 gm and the final weight will be 120 to 125 gm). When you put these beads in a closed space, like a metal or plastic container. The beads start absorbing water from the air, creating a dry environment and maintaining a low-humidity environment.
• When seeds are placed into a container with beads, seeds will lose water due to low humidity around the seed. It will continue until they come to an equilibrium. Hence, it simply transfers the water in the seed to beads through the air, without any need for heat. 
• After 24 hours, the equilibrium will be raised when seeds are kept with zeolite beads in air-tight containers.

Maintain storage condition, vigor, and longevity by a build-in digital hygrometer

How to reactivate or reuse drying Beads?

• Beads can be reused and reactivated by heating them up between 200 o c to 300 o c for 2-3 hours to release the absorbed moisture. (temperature not over 300 o c)
• Cool the beads before reusing it
• Package for storage in air-tight containers.

How to calculate drying beads per kg of seeds?

An example of a bead/seed ratio table (for a given bead capacity – 20%)

PS: corrections (1%) have NOT been added to this table

Also, visit Seed Storage, Types of seed dormancy, Seed Pelleting, and Seed packing materials.

The quantity of beads needed depends on the initial seed moisture content, the desired seed moisture content, and the beads’ capacity. Referring to the Bioversity International chart, let’s figure out how many beads are required per kilogram of seeds for hermetic storage. Take chilli seeds as an example: if the initial seed moisture is 10%, but the desired seed moisture content is 6%, and the beads capacity is 20%, it means we’ll need a total of 21% beads. So, for every kilogram of chili seeds, that’s approximately 210 grams of beads required.

Safety precautions

Do not add beads straight into very wet seeds like melon, cucumber, and tomato seeds immediately after washing. First air-dry and remove excess water before you mix them with the beads.

This can be a risk if it:

• Improper protocol follow-up.
• Improper system testing and its implementation.

Can drying beads damage seeds?

• If you store excess beads with seeds, the moisture content will be reduced to very low levels. Most desiccant-tolerant (Orthodox) seeds aren’t harmed even when dried to 3-5% moisture. However, some larger seeds, like cucumber, watermelon, bottle gourd, and beans, can be damaged by quick rehydration from very low moisture levels, a condition known as imbibition damage.
• For safety, it is a good practice to seeds out of the sealed storage container and allow them to rehydrate in air under normal conditions for a few days before planting or exposing them to liquid water.
• Recalcitrant seeds like mango and durian, palm from tropical trees, and others like citrus, are damaged by drying and shouldn’t be dried using desiccant beads.

How do you know the water-absorbing capacity of beads?

In silica gel changes from white to pink once used.  In Zeolite, beads change color from white to light green color. Other types of humidity indicator devices also be used.

Which is best for seed storage Zeolite beads or silica gel? And why?

Zeolite beads, best for seed storage, show no loss of water-holding capacity after repeated regeneration. But, you observe a loss of water-holding capacity in silica gel. And also no effect on seed quality [Research Paper By Kishore Kumar and JS Hilli]

How do you know if the containers are airtight or not?

Put a small quantity of fresh silica gel in an empty, sealed container.  If its color changes within a few days, that means the container isn’t moisture-proof.

Advantages of using desiccant for ultra-drying of seeds

• Can dry seeds to a specific and low MC (2-3%)
• Protected from molds, insects, and rodents
• Seed quality is preserved for several years
• Conservation of germplasm for a longer period
• No need for cold storage to maintain seed viability
• Dry the seeds to a very low moisture level, without the use of heat. Thus preserving seed quality.
•  Keeping seeds dry during storage can increase seed longevity, germination rates, and plant vigor- ultimately increasing yield capacity for farmers.
• Reuse desiccant
• Real cost saver (no need for expensive equipment like a dryer, or conditioned room.) and it is a time investment.

Cost of drying Beads for seed storage?

The cost of the beads varies from country to country due to import duties and other expenses. Additionally, the approximate price information provided in the table might change depending on market demand.

Description	Unit	Price per Unit
Drying beads	1 kg	17 $
Drying beads 10 kg	10 packs for 1 kg	142 $
Drying beads 25 kg	Single drum of 50 liter	294 $
Dry store
Box 1.6 L (incl. 0.1kg beads)	Set of 24	557 $
Box 8.4 L (incl. 0.5kg beads)	Set of 12	428 $
Box 16 L (incl. 1kg beads)	Set of 12	579 $
Box 72 L (incl. 2 kg beads)	Set of 4	550 $
Box 50 L (incl. 4 kg beads)	Set of 4	964 $
Box 100 L (incl. 8 kg beads)	Set of 4	1253 $